Smart battery with maintenance and testing functions, communications, and display

ABSTRACT

A smart battery that self-monitors and maintains information about itself that includes its state of charge, its need for maintenance, and for conditions that indicate that it has reached the end of its useful life and should be discarded. The information maintained by the battery is then either displayed on an on-board display or is communicated to another device on a communication bus. The state of charge quantifies the smart battery&#39;s ability to reliably deliver charge to a host device and is dynamically adjusted over the lifetime of the smart battery. The state of charge may not exceed a full charge capacity value maintained by the smart battery and initially set to an estimated value. This full charge capacity value is dynamically adjusted throughout the life of the smart battery using information accumulated and maintained by the smart battery that indicates the smart battery&#39;s actual performance during use and by using messages received from a battery maintenance and testing system. The smart battery also accumulates and maintains information that indicates that the smart battery requires maintenance. A battery maintenance and testing system can read this need for maintenance from the smart battery and take the steps necessary to automatically maintain the smart battery. Conditions that indicate that the battery is defective or has exceeded its useful life are also maintained by the smart battery and communicated through the on-board display or to another devices over a communication bus. The battery is specially configured for easy assembly.

RELATIONSHIP TO OTHER APPLICATIONS

This application is a continuation and claims the benefit of priorapplication Ser. No. 09/237,193, filed Jan. 26, 1999, now U.S. Pat. No.6,072,299, which in turn claims the benefit of U.S. ProvisionalApplication Serial No. 60/072,485 filed Jan, 26, 1998. The disclosureand drawings of application Ser. No. 09/237,193 and ProvisionalApplication Serial No. 60/072,485 are specifically incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates generally to the field of rechargeablebatteries, and more particularly to an intelligent battery thatinternally monitors its own operating condition, its own need formaintenance, and its own useful life, and communicates this informationto a user or to an intelligent device.

BACKGROUND OF THE INVENTION

With the proliferation of portable electronic devices, the use ofrechargeable batteries has become increasingly important. Rechargeablebatteries can now be found in devices as simple as a flashlight, asimportant as notebook computers, and as vital as portable medicalequipment. An example of a portable medical device which is dependent ona rechargeable battery pack is a portable defibrillator unit.

Portable defibrillator units are used by emergency medical technicianson persons suffering from certain types of abnormal heart rhythms, e.g.,ventricular fibrillation, to shock the heart back into a normal beatingpattern. Although many of these portable defibrillators have the abilityto operate off of AC line current, when used in the field, portabledefibrillators are almost totally dependent on rechargeable batterypacks. The portable battery packs provide the power both to operate theinternal electronics of the defibrillator and to provide the chargesource for the therapeutic shock. In order to provide the power sourcefor charging the shock delivery circuitry of the defibrillator, it isnecessary that the portable battery pack be capable of providing arelatively large current draw over a relatively short period of time. Ifthe battery is unable to supply this current when demanded, the deliveryof the therapeutic shock may be delayed or prohibited.

Seconds count in the application of the therapeutic shock to a personsuffering a heart attack. Swapping a bad battery pack in and out of adefibrillator may waste this precious time, as may waiting for amarginally functional battery to deliver the charge necessary for thetherapeutic shock. It is important, therefore, for the user of aportable defibrillator to make sure that a reliable, working batterypack is available. This has usually meant having an ample supply ofextra battery packs on hand. Unfortunately, one can usually only guessthe battery pack's ability to reliably deliver high current chargingpulses. While users normally log the age and use of the battery manuallyto predict its current condition, the accuracy of the predictions areboth dependent on the accuracy of the records and the validity of theunderlying assumptions of the predictions.

In response to the demand for reliable batteries, computer and batterymanufacturers have recently been developing “smart batteries” whichinternally measure battery variables such as voltage and current flow inand out of the battery and then apply predictive algorithms to estimatethe battery's state of charge. The battery's predicted state of chargecan then be communicated to a portable electronic device such as anotebook computer (i.e., a “host”) over a communication bus. This isuseful in applications where a computer needs to find out if there isenough charge in the battery to save a word-processing file to a diskdrive. However, the prediction of a smart battery's state of charge mustbe much more reliable in medical device equipment, such as adefibrillator, where the state of charge is crucial to the appropriatemedical treatment of an individual. This is particularly true if theonly way to determine if the battery is able to deliver the charge is byfirst inserting it into the host unit.

The basic method for keeping track of the state of charge (“SOC”) of asmart battery is to create a coulomb counter that adds the electronsgoing in and subtracts the electrons going out from a running counter.However, energy that goes into the battery does not all end up as storedcharge—some of it is expended as heat in the charging process. For thisreason an ‘Efficiency Coefficient’ (EC) is used to maintain theaccounting. An EC can be estimated based on testing a statisticallysignificant sample of batteries and choosing a value that represents theworst case battery. One method devised by the industry to avoid theerror in calculating SOC is to establish a value for a fully chargedbattery and then cease accounting for the charge once the calculatedcharge has reached this value, regardless of measured input current.

The ability of a battery to deliver its charge on demand depends both onbattery charge and proper battery maintenance. Rechargeable batterypacks are currently manufactured using a number of known batterychemistries, including nickel cadmium (NiCd), sealed lead acid (SLA),nickel-metal hydride (NiMH), lithium ion (Li-ion), lithium polymer(Li-polymer), and rechargeable alkaline. The most popular choice forrechargeable batteries is currently the NiCd chemistry because it isrelatively inexpensive, is fast and easy to charge, has excellent loadperformance even at cold temperatures, and is capable of withstanding ahigh number of charge/discharge cycles. Over the course of the life ofthe NiCd battery, however, the cycling of the battery causes it todevelop crystalline formations that substantially decreases thebattery's ability to hold charge. This is commonly referred to as“memory”. It is known that “conditioning” the battery, which involvesfully discharging the battery and then charging the battery back to thestate of full charge, can substantially reduce NiCd memory. This processhelps breakdown the crystalline structure developed over time andenables the battery to receive and store a greater charge.

If the NiCd “memory” goes undetected, the battery may show a voltagethat indicates a full charge while it actually does not hold sufficientcharge to supply the high current pulse required by a demandingapplication such as a portable defibrillator. While this “memory”problem has long been recognized, the conditioning required to correctit has depended on the user manually conditioning the battery on aregular basis. This meant that the user had to estimate when the batteryrequired conditioning and then manually put the battery through aconditioning process. The actual discharging and charging of the batteryduring conditioning can take hours during which the battery is out ofservice. Due to these limitations, rechargeable battery packs aresometimes used past the period in which they should be conditioned, useduntil they fail, or are simply discarded much earlier than they wouldactually need to be if they were properly maintained.

Accordingly, a method and apparatus for a rechargeable battery pack thatinforms the user that the battery pack is ready to use, requiresmaintenance, or should be discarded, is needed. Further, the method andapparatus should be able to communicate with an intelligent batterymaintenance and testing system that can charge, condition, and test thebattery in accordance with the information that the battery maintains.As explained in the following, the present invention provides a methodand apparatus that meets these criteria and solves other problems in theprior art.

SUMMARY OF THE INVENTION

In accordance with the present invention, an intelligent battery isprovided which is capable of self-monitoring its state of charge, itsneed for maintenance, and the end of its useful life. The batteryincludes a user interface and display through which informationregarding the state of charge, maintenance requirements and end ofuseful life can be displayed to a user or requested by a user by pushinga depressible keypad. In addition, the battery includes a monitoringcircuit for self-monitoring that includes a communication interface forcommunicating this information to another device.

In one embodiment of the present invention, the monitoring circuit ofthe intelligent battery comprises an internal circuit board connected bya plurality of conductive rods to a plurality of external communicationinterface pads and a plurality of external voltage terminals locatedalong a longitudinal axis that is near an edge of a bottom surface ofthe battery, such that the external communication interface pads arelocated between the external voltage terminals. The externalcommunication interface pads electrically couple the battery to anotherdevice so that the battery may communicate with the other device.Further, the circuit board, conductive rods and external communicationinterface pads are positioned such that a lighted display and amomentary contact switch disposed on the upper surface of the circuitboard are aligned directly beneath the user interface and display andthe depressible keypad, respectively, disposed on a top surface of thebattery. This arrangement allows the conductive rods to ascend throughthe interior of the battery to secure the placement of the circuit boardbeneath the user interface and display and electrically couple thecircuit board to the external communication interface pads.

In accordance with other aspects of the invention, the circuit board ofthe battery includes a processing unit coupled to a non-volatile memoryand a communication interface. The non-volatile memory stores theprogram code necessary for monitoring the battery, storing monitoredinformation and communicating this information via the communicationinterface. More specifically, the information monitored and stored inthe non-volatile memory includes: the full charge capacity of thebattery; the time expired since the last successful battery condition;the total number of charge/discharge cycles; the number ofcharge/discharge cycles since the last condition; and the amount of timethat the battery has operated in a temperature range that exceeds arecommended maximum temperature; a log of critical errors; and a set offlags indicating non-critical errors.

In accordance with yet other aspects of the present invention, thebattery uses the monitored information to perform a plurality of testsfor determining if the battery is in working condition, if the batteryneeds maintenance, or if the battery needs to be discarded. Once thetests are performed, the battery may communicate the results to anotherdevice, such as a battery maintenance and testing system, in order toreceive the appropriate maintenance, or the results of the tests may beoutput on the lighted display and thus, communicated to the user.

In accordance with other aspects of the invention, the smart batterydynamically calculates its state of charge, which it stores in itsmemory as a state of charge value (SOC). The SOC is individuallyadjusted for each smart battery, throughout the life of that smartbattery, by a method of the invention that compares the computed SOC(maintained by the smart battery) with an actual state of charge asdetermined by a battery maintenance and testing system When charged bythe battery maintenance and testing system, the smart battery updatesits state of charge value (SOC) until the battery maintenance andtesting system determines that the smart battery is no longer acceptingcharge. When fully charged, the battery maintenance and testing systemsends an End of Charge message to the smart battery which then sets itsSOC to a full charge capacity value (FCC) that is also maintained in thesmart battery's memory. During maintenance of the smart battery, thefull charge capacity value (FCC) is adjusted by the smart battery whenthe battery maintenance and testing system sends an End of Dischargemessage to the smart battery to reflect any discrepancy between the SOCand the actual measurement of the state of charge made by the smartbattery maintenance and testing system.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an elevated perspective view of an upper portion of a batteryformed in accordance with a first embodiment of the present invention;

FIG. 2 is a perspective view of a bottom portion of the battery shown inFIG. 1;

FIG. 3 is a perspective view of the battery shown in FIG. 1 with theupper portion removed and the contents of the battery exposed, includingan internal circuit board;

FIG. 4 is a partial, cross-sectional view of the battery shown in FIG. 3taken along the line 4—4 and exposing a communication interface assemblyformed in accordance with the present invention;

FIG. 5 is a perspective view of a bottom portion of a battery formed inaccordance with a second embodiment of the present invention;

FIG. 6 is a block diagram of the internal circuit board shown in FIG. 3;

FIG. 7A is a flow chart illustrating the logic used by the battery ofthe present invention to monitor and test itself;

FIG. 7B is a flow chart illustrating the logic used by the battery ofthe present invention to monitor its state of charge during charging;

FIG. 7C is a flow chart illustrating the logic used by the battery ofthe present invention to monitor its state of charge during discharge;

FIG. 8 is a flow chart illustrating the logic used by the battery of thepresent invention to monitor and test for battery discard;

FIG. 9 is a flow chart illustrating the logic used by the battery of thepresent invention to monitor and test for battery maintenance;

FIG. 10 is a flow chart illustrating the logic used by the battery ofthe present invention to display the battery's condition to a user;

FIG. 11 is a flow chart illustrating the logic used by the battery ofthe present invention to report the battery's condition to anotherdevice; and

FIG. 12 is a flow chart illustrating the logic used by the battery ofthe present invention after the battery has been notified that thebattery has been successfully conditioned.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An “intelligent” or “smart” battery 22 formed in accordance with thepresent invention is shown in FIG. 1. The battery 22 has a housing 24that is comprised of an upper portion 26 and a base portion 28. A userinterface and display area 32 for displaying battery information to auser and for receiving requests from the user is disposed near a forwardportion 30 of the upper portion 26. The user interface and display area32 is comprised of a depressible keypad 34 and an opaque window section36. Shown in phantom within the opaque window 36 are four channels 38that segment the opaque window into four separate display zones 38 a, 38b, 38 c, 38 d. The opaque window 36 is preferably shaped like a batteryto indicate to the user that it displays the condition of the battery.The top cover 26 also has a display area 40 where product andmanufacturer identification or instructions for the use of the smartbattery can be placed.

A bottom view of the battery 22 is shown in FIG. 2. The base portion 28has a bottom face 42, a first end 48, side faces 46 and a second end 44.A first voltage receptacle or aperture 50 and a second voltagereceptacle or aperture 52 are located on the bottom face 42 near thebottom face's intersection with the second end 44. The first and secondvoltage receptacles 50 and 52 are aligned upon a longitudinal axis 54 inparallel with the intersection of the bottom face 42 and the second end44. Also located on the bottom face 42 along the longitudinal axis 54and between the first and second voltage receptacles 50 and 52 are threecommunication interface pads 56 (also referred to as circular conductivecontacts), which electrically couple with another device, such as abattery maintenance and testing system, so that the battery 22 maycommunicate with the other device. Two indented display areas 57 and 58are provided for the placement of identification, registration andinstruction stickers.

In FIG. 3, the upper portion 26 of the battery 22 has been removedexposing a monitoring circuit 71 deposited in an interior portion 60 ofthe base portion 28 of the battery 22. The interior portion 60 alsocontains ten nickel cadmium battery cells connected in series andgrouped together in five cell tubes 62. The battery cell tubes 62 areheld in position by two pieces of foam core tape 64 on the top and twobelow (not shown) adhering the cells 62 to the base portion 28. Themonitoring circuit 71 includes a circuit board 66, which rests above thebattery cell tubes 62 upon the foam core tape, and five conductive rods68 coupled to the circuit board 66 near its forward edge 70. A wire 78electrically couples the negative terminal of a first battery cell withthe circuit board 66. As will be described in more detail below, theconductive rods 68 secure the circuit board 66 directly below the userinterface and display area 32 disposed on the top cover 26 of thebattery 22 and directly above the communication interface pads 56.

The electrical and mechanical effect of the connection of the circuitboard 66 to the conductive rods 68, i.e., of the monitoring circuit 71,will now be discussed in more detail with reference to FIG. 4. FIG. 4 isa cross-sectional view of the battery 22 along line 44 of FIG. 3. It canbe clearly seen from this view that the alignment of first voltagereceptacle 50, the second voltage receptacle 52 and the threecommunication interface pads 56 along the longitudinal axis 54advantageously allows the conductive rods 68 to serve as the structuralsupport that holds the circuit board 66 in position directly below theuser interface and display area 32 and directly above the communicationinterface pads 56. In this regard, a lower portion 82 of each conductiverod 68 is molded into a circular plastic well 84 that is part of thebottom face 42 of the base portion 28. Each conductive rod 68 also has arigid intermediate portion 86 and a top portion 88 that is soldered to aconductive pad 90 on circuit board 66. During assembly, the circuitboard 66 is soldered into position with the forward edge 70 of thecircuit board 66 resting on support walls 92 that are part of the baseportion 28 of the battery 22, and a rear end 94 of the circuit boardresting upon the foam core tape 64 and battery cell tubes 62.

As noted above, each conductive rod 68 couples a communication interfacepad 56 or a voltage receptacle 50 or 52 on the bottom face 42 of thebattery 22 to the circuit board 66. The rigid intermediate portion 86 ofthe conductive rod 68 for the first voltage receptacle 50 is alsocoupled to the battery cells 62 by a soldered lead 96. The first voltagereceptacle 50 and the second voltage receptacle 52 include a blind hole98 for the reception of a banana plug from a defibrillator, a batterymaintenance and testing system or some other device which passes currentfrom or to the battery 22.

Each communication interface pad 56 may be electrically coupled with ahost defibrillator, a host battery maintenance and testing system, orsome other host device equipped with compatible communication interfacehardware and software so that the communication interface pad maycommunicate certain signals to and from the host device. In an actualembodiment of the present invention described herein, one of thecommunication interface pads 56 communicates a CLOCK signal, anothercommunicates a DATA signal, and the last communicates a THERMISTORsignal. Consequently, the respective conductive rods 68 electricallycouple the CLOCK signal, DATA signal and THERMISTOR signal to thecircuit board 66.

The circuit board 66 is positioned directly beneath the user interfaceand display area 32 when the upper portion 26 of the battery 22 isplaced in position over the base portion 28. Consequently, when a userpushes the depressible keypad 34 of the user interface and display area32, contact is made with a momentary contact switch 72 (FIG. 3), whichis mounted on the upper surface 74 of the circuit board 66 and alignedbelow the depressible keypad 34 (FIG. 1). The circuit board 66 alsoincludes a lighted display 76 consisting of four light emitting diodes(LED's) 76 a-d, which is positioned on the upper surface 74 of thecircuit board 66 so that the four LED's 76 a-d align directly below thefour corresponding channels 38 a-d of the opaque window 36 disposed onthe top cover 26 of the battery. Consequently, when the user pushes thedepressible keypad 34, a state of charge of the battery is output on theLED's 76 a-d of the display 76 and seen by the user through thecorresponding channels 38 a-d of the user interface and display area 32.As can be appreciated from the preceding description, the precisealignment of the circuit board 66 is important in order to position themomentary contact switch 72 below the depressible keypad 34 and theLED's of the lighted display 76 below their corresponding channels 38 inthe opaque window 36.

Another embodiment of a “smart” battery 22′ is shown in FIG. 5. Thebattery 22′ is essentially the same as the battery 22 shown in FIGS. 1-3except that it does not include the user interface and display area 32or the communication interface pads 56. Rather, the battery 22′substitutes a blade connector 130 at an opposite end of the battery 22′for the communication interface pads 56 used in the first embodiment ofthe smart battery 22. The battery 22′ includes an upper portion 124 anda base portion 126 with a bottom face 128 and a first end 132. The shapeof the upper portion 124 is configured to accommodate sealed lead acid(SLA) battery cells. The shape of the upper portion 124, however, isunimportant to the operation of the battery 22, or 22′ and can bemodified to accommodate any battery cell type or chemistry. It willfurther be appreciated that in other embodiments of the presentinvention, a user interface and display area 32 may be disposed on theupper portion 124 of the battery 22′.

A first voltage receptacle or aperture 50′ and a second voltagereceptacle or aperture 52′ are aligned along a longitudinal axis 54′parallel to the intersection of a second end 133 and the bottom face128. The blade connector 130 is provided at the intersection of a firstend 132 and the bottom face 128. The blade connector 130 provides a pathfor coupling a CLOCK signal 134, a DATA signal 136, and a THERMISTORsignal 138 to an internal circuit board connected by a series of wires(not shown). It will be appreciated that the internal circuit boardemployed by the second embodiment of the battery 22′ is essentially thesame as the circuit board 66 employed by the first embodiment of thebattery 22.

The components that comprise the monitoring circuit 71 are shown inblock form in FIG. 6. The monitoring circuit 71 includes a centralprocessing unit (“CPU”) 140 that is coupled to the momentary contactswitch 72, the lighted display 76, a non-volatile memory 142 and acommunication interface 144. The communication interface 144 is used tocommunicate information between the battery 22 and a host defibrillator,battery maintenance and testing system or other device. In the actualembodiment of the present invention described herein, the communicationinterface 144 communicates with external devices in accordance with abidirectional communication bus standard known as SMBus. The SMBusstandard is more specifically described in the System Management BusSpecification (Revision 1.0 Feb. 15, 1995) developed by a consortium ofbattery and computer manufacturers and incorporated herein by reference.The SMBus standard uses an I²C bus as its backbone, which is discussedin detail in the document entitled The I ² C Bus and How to Use it byPhilips Semiconductors and incorporated by reference herein. The actualcommunication between the battery 22 and other devices is discussed indetail in commonly owned U.S. patent application Ser. No. 09/013,409,entitled BATTERY MAINTENANCE AND TESTING SYSTEM filed concurrentlyherewith, the disclosure and drawings of which are incorporated hereinby reference.

The battery 22 monitors its voltage by using a voltage measuring circuit141, a current measuring circuit 143 and temperature measuring circuit145 that are all connected to an analog-to-digital (“A/D”) converter 147that is coupled to the CPU 140. The current measuring circuit 143computes the current flowing through a reference resistor which isproportional to the voltage across the Vsense resistor 149. Thetemperature measuring circuit 145 employs a thermistor and the voltagemeasuring circuit 141 is measured across the battery cell voltageterminals 50 and 52.

Now that the components of the monitoring circuit 71 have beendescribed, the program code stored in the non-volatile memory 142 andexecuted by the central processing unit 140 will be discussed in moredetail. In this regard, FIG. 7A illustrates the main processing routine146 used by the central processing unit 140 to monitor and test thebattery 22. The logic begins in a block 146 and then proceeds to a block148 where it determines the batterys state of charge. The logic employedby the battery 22 to monitor its state of charge will be described inmore detail below in connection with FIGS. 7B and 7C. It thenincrements, in a block 149, a counter which keeps track of the timesince the smart battery 22 was last conditioned. In a decision block150, the logic determines if the battery 22 has been cycled (charged anddischarged). If so, the cycle counter is incremented in a block 151. Ifthe result of decision block 150 is negative, the logic proceeds to adecision block 152 where it determines if the battery is operating at atemperature that is above a predefined maximum temperature. If so, atime over temperature counter is incremented in a block 153. Otherwise,the logic proceeds to a block 154 where it checks for and logs criticalerrors that would indicate the battery needs to be discarded. The logicused by the smart battery to check for and log critical errors isdiscussed in more detail below in reference to FIG. 8. The battery thenchecks for and flags non-critical errors indicating the need formaintenance in a block 155, which will be described in more detail belowin reference to FIG. 9. If at any time the user pushes the depressiblekeypad 72 or if the battery was removed from the battery maintenance andtesting system, this is detected in a decision block 156 and the batterydisplays its condition in a block 157 by lighting the appropriate LED's76 a-d of the lighted display 76 in predefined patterns that indicatethe status of the smart battery 22. If the depressible keypad has notbeen pushed, or if it has been pushed and the battery conditiondisplayed, the main logic depicted in FIG. 7A is repeated.

The present invention also improves upon the accuracy of keeping trackof the battery's state of charge (SOC). It has been found that theefficiency coefficient (EC) is different depending upon the state ofcharge of the battery—higher at the beginning of the charge cycle, lowerat the end. Additionally, variations within the process of constructingthe battery influence the EC such that there is a distribution of ECvalues even within a single manufacturer's product. Therefore, applyinga constant EC for all batteries of a certain type as is done in thesimple EC method found in the background art for calculating SOC issusceptible to inaccuracies caused by actual variations in the EC thatoccur during the charge cycle; inaccuracies caused by variations inbattery construction; and inaccuracies caused by conservatively choosinga worst case value as an EC. It also should be appreciated thatinaccuracies that are introduced into the running SOC total arecumulative, meaning that any variations in estimated SOC will accumulatefrom charge cycle to charge cycle.

The present invention's method for computing a SOC with a higheraccuracy than believed possible in the prior art includes establishingtwo thresholds that the SOC is updated within. These two thresholds areset by messages communicated by a battery maintenance and testing systemto the smart battery 22 via the communication interface 144. The firstthreshold is set in response to an End of Discharge detected by thesmart battery 22 when the battery maintenance and testing system detectsa minimum voltage associated with the battery chemistry. After detectingthe End of Discharge, the smart battery 22 resets the SOC to a minimumcharge value. In an actual embodiment, the minimum charge value is zero.The smart battery 22 also sets the FCC value to the full charge capacityof that individual battery determined through actual experience withthat battery by adjusting the FCC by adding to it whatever residualamount that remained in the SOC at the time the End of Discharge messagewas received by the smart battery 22 from the battery maintenance andtesting system.

The second threshold is set in response to an End of Charge message sentby the battery maintenance and testing system to the smart battery 22.The battery maintenance and testing system employs charge algorithmsthat monitor the charge waveforms of the batteries as they are beingcharged. Based on this monitoring, the battery maintenance and testingsystem sends an End of Charge message when it determines that a batteryis fully charged. Many suitable charge algorithms are well known in theart and may be used for this purpose. In response to the End of Chargemessage, the smart battery 22 immediately resets its SOC to thedynamically adjusted full charge capacity (FCC) value (discussed above)that is stored in the smart battery's non-volatile memory 142 and thenstops counting charge current supplied to the smart battery 22. In thisway, the smart battery has the ability to dynamically re-calibrate itsSOC register at either end of the charge/discharge cycle usinginformation maintained by the smart battery regarding the actual stateof charge of that individual battery instead of the “one size fits all”approach taken in the prior art.

Another of the factors that affect the accuracy of the SOC is selfdischarge experienced by the smart battery 22 as a result of its owninternal resistance. As this discharge is internal to the cells, it isimpossible for the smart battery 22 to measure and therefore must beestimated. Statistical testing can be used to establish the expectedself discharge rate for a specific manufacturer's cell and these valuescan be incorporated into an algorithm. Unfortunately the self dischargerate is temperature dependent, so the temperature of the cell must bemeasured to adjust the self discharge rate to compensate fortemperature. What can't be estimated is the changes in self dischargethat occur as a cell ages or begins to fail. An unexpected increase inself discharge would cause the SOC to become inaccurate—possiblyindicating more capacity than actually exists in the smart battery 22.To mitigate the effect of a changing self discharge rate on the accuracyof the SOC, the present invention disables the SOC display by recordinga critical error in the smart battery's non-volatile memory 142 after apredefined number of cycles (precluding the possibility of old age). Thepresent invention also mitigates the effect of self discharge on the SOCby monitoring the amount of discrepancy attributed to self discharge anddisabling the SOC display by recording a critical error in the smartbattery's non-volatile memory 142 once the self discharge exceeds apredefined self discharge threshold. This second method is performedevery time the battery is discharged in accordance with the methoddiscussed below with reference to FIG. 7C. As is discussed in moredetail below, if the residual value in the SOC is a positive number whenthe End of Discharge message is received by the smart battery from thebattery maintenance and testing system, it means that there isunaccounted self discharge occurring. If this value exceeds a predefinedself discharge threshold (that allows for minor variations in the chargecycling) the battery will log a critical error effectively ending itslife.

The smart battery 22 continuously monitors its ability to reliablydeliver charge as is illustrated in FIG. 7A The SOC of the battery isupdated in a block 148 according to the methods illustrated in FIGS. 7Band 7C. When the smart battery 22 is being charged in a batterymaintenance and testing system the state of charge is adjusted accordingto the method shown in FIG. 7B, which is entered at a block 300. In adecision block 302, the smart battery 22 checks to see if an End ofCharge message has been received on the communication interface 144.This message is sent by the battery maintenance and testing system whenthe charging algorithms of the battery maintenance and charging systemdetects that the battery has received its full state of charge. Untilthis message is received, the smart battery 22 updates its state ofcharge in a block 304 using equation (1):$\underset{\_}{{Equation}\quad 1\text{:}\quad {Charging}\quad {SOC}\quad {equation}}$${SOC}_{1} = {{SOC}_{0} + {\left\lbrack \frac{E_{C} \cdot \left( {I_{C1} + I_{C0} - I_{B1} - I_{B0}} \right) \cdot \left( {t_{1} - t_{0}} \right)}{7200 \cdot C_{nom}} \right\rbrack {}_{{SOC}_{0} < {FCC}}}}$

In this equation:

SOC₁ is the present value of the calculated SOC in percent. This valueis calculated.

SOC₀ is the prior value of the calculated SOC in percent. This value iscalculated.

E_(C) is the efficiency of charge acceptance in percent. This value is aconstant, based on temperature and current.

I_(C1) is the present charge current into the battery in amperes. Thisvalue is measured and is assumed to include the bias current I_(B1).

I_(C0) is the prior charge current into the battery in amperes. Thisvalue is measured and is assumed to include the bias current I_(B0).

I_(B1) is the present bias current for the electronics in the batterypack in amperes. This value is measured or estimated.

I_(B0) is the prior bias current for the electronics in the battery packin amperes. This value is measured or estimated.

t₁ is the present time of the measurements in seconds. This value ismeasured.

t₀ is the prior time of the measurements in seconds. This value ismeasured.

7200 is a constant conversion factor accounting for averaging thecurrents, efficiency in percent, time in seconds, and capacity in amphours.

C_(nom) is the battery manufacturer's capacity rating in amp hours. Thisvalue is a constant.

FCC is the full charge capacity.

Equation 1 is essentially integrating the net current flowing into thebattery and adjusting this for the battery's ability to absorb charge.The smart battery 22 continues to monitor its state of charge duringcharging by returning to block 300. When the battery maintenance andtesting system detects that the smart battery 22 is no longer acceptingcharge, the battery maintenance and testing system sends an End ofCharge message, which the smart battery 22 recognizes in decision block302. The smart battery 22 responds by resetting its state of charge tothe full charge capacity (FCC) value which is stored in the nonvolatilememory. In this way, the state of charge never exceeds the theoreticalfull charge capacity value. Control returns in a block 308 to the mainprocessing loop after the End of Charge message is received from thebattery maintenance and testing system. If the battery is removed fromthe battery maintenance and testing system before it has been fullycharged or the smart battery 22 was charged in a charging unit that doesnot support the End of Charge message, the SOC calculated with EquationI is maintained by the smart battery 22 without the benefit of beingcalibrated to the FCC value until the next time the smart battery 22 isfully charged in the battery maintenance and testing system.

The method in FIG. 7C is executed beginning in block 310 when the smartbattery is being discharged. While the smart battery 22 is waiting todetect an End of Discharge in a decision block 312, the smart batteryupdates the state of charge in a block 314 using equation (2):$\underset{\_}{{Equation}\quad 2\text{:}\quad {{Disch}{arging}}\quad {SOC}\quad {Equation}}$${SOC}_{1} = {{SOC}_{0} - \left\{ {K_{T} \cdot E_{D} \cdot \left( \frac{I_{D1} + I_{D0} + I_{B1} + I_{B0}}{2} \right) \cdot \left( \frac{t_{1} - t_{0}}{3600 \cdot C_{nom}} \right)} \right\}}$

In this equation:

SOC₁ is the present value of the calculated SOC in percent. This valueis calculated.

SOC₀ is the prior value of the calculated SOC in percent. This value iscalculated.

K_(T) is the temperature coefficient of discharge current and has nounits. This value is calculated and is equal to 1 in one embodiment.

I_(D1) is the present charge current into the battery in amperes. Thisvalue is measured and is assumed to exclude the bias current I_(B1).

I_(D0) is the prior charge current into the battery in amperes. Thisvalue is measured and is assumed to exclude the bias current I_(B0).

I_(B1) is the present bias current for the electronics in the batterypack in amperes. This value is measured or estimated.

I_(B0) is the prior bias current for the electronics in the battery packin amperes. This value is measured or estimated.

E_(D) is the efficiency of discharge in percent.

t₁ is the present time of the measurements in seconds. This value ismeasured.

t₀ is the prior time of the measurements in seconds. This value ismeasured.

2 is a constant conversion factor accounting for averaging the currents.

3600 is a constant conversion factor accounting for time in seconds andcapacity in amp hours.

C_(nom) is the battery manufacturer's capacity rating in AH. This valueis a constant.

For a smart battery 22 of the NiCd type, the smart battery 22 continuesmonitoring its state of charge by returning to the block 310 until itdetermines that it has reached an End of Discharge in block 312. In anactual embodiment of the invention, the smart battery determines that ithas reached its End of Discharge when it has reached a terminal voltageof 10 volts. After the End of Discharge is detected in block 312, thesmart battery 22 checks to see if the state of charge (SOC) that it hascalculated is positive and if it exceeds a predefined error margin valuein decision block 316. If the state of charge is positive, thisindicates that there is a higher level of self discharge than isexpected, thus indicating that the battery has reached the end of itsuseful life. In this case, the smart battery 22 logs an excessive selfdischarge critical error in a block 318 and then returns control themain processing loop (FIG. 7A) in a block 320. If, however, the state ofcharge either equals zero or is negative as detected in decision block316, then the full charge capacity value FCC maintained in non-volatilememory is adjusted by adding the state of charge value (which is zero ora negative value) to its current value in a block 322. This has theeffect of adjusting the full charge capacity FCC to reflect the actualcapacity of the battery based on actual experience with the battery.Before the full charge capacity value FCC is adjusted, however, fourtests are administered to check that the value in the SOC is probablynot in error. The four tests that must first be passed are: (1) has thebattery discharged to a minimum voltage from a fully charged state in ablock 324; (2) has the battery not been partially charged during thedischarge in a block 326; (3) is the accumulated self discharge lessthan 15% of the full charge capacity in a block 328; and (4) has thebattery temperature not exceeded 50° C. during discharge in a decisionblock 330. If the answer to any of these four tests 324, 326, 328 and330 is no, then control is returned to the main processing loop in theblock 320. Otherwise, the full charge capacity in nonvolatile memory isreset to its former value plus the state of charge value SOC in block322 (which is 0 or a negative value), and then the state of charge valuemaintained by the smart battery 22 is set to zero (indicating thebattery has been fully discharged).

For a smart battery 22 based on the SLA chemistry, the end of dischargeis reached when the smart battery 22 reaches a State of Charge ofapproximately 25% of its full charge capacity when it has an internalimpedance of about 0.128 Ohms. This value has been derived empirically.This internal impedance, under a normal operating load of 1 amp,corresponds to a terminal voltage of 11.7 volts. This terminal voltageis used for the nominal low battery threshold. If however the currentvaries from 1 Amp the following formula is used:V(threshold)=11.7−((I(measured)−I(nom))*0.128) where I(nom) in this caseis 1 Amp.

The routine for checking for and logging critical errors 154, i.e.,errors indicating that the smart battery should be discarded, is shownin FIG. 8. In a block 158, the battery 22 checks the total number ofcycles that it has been through against a maximum number of cycles thatthe battery can theoretically withstand. For example, if the battery 22is a NiCd battery, in an actual embodiment of the invention, thismaximum number is 750 cycles. The number of cycles used for the maximumnumber of cycles permitted may vary according to the actual battery cellused and may be determined, for example, from data provided by themanufacturer of the battery cell or by actual product testing of thebattery cell. Therefore, if the total cycles experienced by the batteryexceeds a maximum number, the battery logs in non-volatile memory 142 amaximum cycles critical error and date stamp in a block 160. The batterythen checks in a block 162 if a maximum lifetime of the battery has beenexceeded. In one embodiment of the invention, the maximum lifetime of abattery is set at three years. If this maximum lifetime has beenexceeded, then a maximum lifetime exceeded critical error is logged inthe non-volatile memory 142 in a block 164.

The battery 22 is also continuously monitoring its self-discharge, as isdiscussed above. Therefore, in a decision block 166, if thisself-discharge exceeds a predetermined limit, an excessiveself-discharge critical error is logged in the non-volatile memory 142in a block 168. The self discharge rate is time and temperaturedependent. For example, to account for self-discharge, the SOC isadjusted for a NiCd smart battery 22 according to the followingformulas: when the temperature of the smart battery 22 is less than 30 Cand the time since the last End of Charge message is less than 24 hours,the formula used is: SOC₁=SOC₀−((SOC₀*0.15)/24). If the time is greaterthan 24 hours since the End of Charge message is sent, thenSOC₁=SOC₀−((SOC₀*0.03)/24). For temperatures more than 30 C, if the timesince last End of Charge is greater than 24 hours thenSOC₁=SOC₀−((SOC₀*0.22)/24). If the time is greater than 24 hours thenSOC₁=SOC₀−((SOC₀*0.05)/24).

The battery 22 may also periodically perform a CRC check of the contentsof the non-volatile memory 142 and verifies the value computed by thisCRC check against a known value to determine if the program contentsstored in the non-volatile memory have been corrupted in a decisionblock 170. If these contents are found to be corrupted, a memorycorrupted critical error is logged in the non-volatile memory in a block172. It is also possible that a host defibrillator, battery maintenanceand testing system, or other device with which the battery iscommunicating has detected a critical error in the battery 22.Consequently, in a decision block 174, the logic determines if a discardnotification has been received from such a device. If so, the battery 22logs a corresponding critical error in the non-volatile memory in ablock 176. The battery also periodically checks the full charge capacityin a decision block 177 and logs a capacity too low critical error in ablock 179 if the full charge capacity is below a predefined limit. In anactual embodiment of the invention, the predefined limit is set to 80%of the nominal Full Charge Capacity. Processing then returns to the mainprocessing routine 146 (FIG. 7A) in a block 178.

The routine for checking and flagging non-critical errors 155, i.e.,errors indicating that the smart battery 22 requires maintenance, isshown in FIG. 9. In a decision block 180 the smart battery 22 checks ifthe number of cycles since the last conditioning of the smart battery 22has exceeded a predefined number of cycles for which conditioning isrecommended. The predefined number of cycles is 90 cycles in oneembodiment of the present invention. If the cycles counted by the smartbattery 22 since the last conditioning have exceeded this predefinednumber of cycles value, then a cycles conditioning recommended flag isset in the non-volatile memory 142 in a block 182. The number of cyclessince last conditioning is then compared against a predefined number ofcycles after which conditioning is required in a decision block 184. Inone embodiment of the present invention this predefined number of cyclesvalue is 180 cycles. If this predefined number of cycles value has beenreached, a cycles conditioning required flag is set in the non-volatilememory 142 in a block 186.

In a decision block 188, the time since the last conditioning iscompared against a predefined interval for which conditioning isrecommended. This predefined interval is 90 days in one embodiment ofthe present invention. If the time since the last conditioning exceedsthis predefined interval, then a time conditioning recommended flag isset in the non-volatile memory 142 in a block 190. In a decision block192, the time since the last conditioning is then compared against apredefined interval for which conditioning is required. In oneembodiment of the present invention, this predefined interval is 180days. If the time since last conditioning recorded by the smart battery22 exceeds this predefined interval, then a time conditioning requiredflag is set in the non-volatile memory 142 in a block 194.

The smart battery 22 checks to see if it has operated over temperaturefor a period that is longer than a predefined time over temperaturevalue in a decision block 196. In one embodiment of the invention, thispredefined time over temperature value is five hours operating in atemperature range that exceeds 50° C. If the time over temperaturerecorded by the smart battery has exceeded the predefined time overtemperature value, a temperature conditioning required flag is set in ablock 198. A microprocessor reset is detected in a decision block 201.If the microprocessor resets, a microprocessor reset flag is set in ablock 203. All of these flags, or non-critical errors, are recorded innon-volatile memory 142 and then operation is returned to the mainprocessing routine loop 146 (FIG. 7A) in a block 200. Those of ordinaryskill in the art will appreciate that the time intervals and cyclethresholds referred to above may vary depending on battery chemistry andcharging techniques.

FIG. 10 illustrates the routine used by the battery 22 to display itscondition to a user who has requested the same by pushing thedepressible keypad 34 of the user interface and display area 32. Thebattery first determines in a block 202 if any critical errors have beenlogged in its non-volatile memory 142. If any such error has beenlogged, the lighted display 76 indicates that the battery is “dead” orneeds to be discarded by lighting the LED's 76 a-d in a discard patternin a block 204. In an actual embodiment of the present invention, adiscard condition is indicated by not lighting any LED's in response tothe user's request.

Returning to decision block 202, if no critical errors are found innon-volatile memory 142, then the battery 22 checks in a decision block206 if the cycle conditioning required flag has been set. If so, thebattery 22 lights the LED's 76 a-d of the lighted display 76 in aconditioning required pattern in a block 212. Otherwise, in a decisionblock 208 it is determined if the time conditioning required flag hasbeen set. If so, the battery lights the LED's 76 a-d in a conditioningrequired pattern in block 212. Otherwise, in a decision block 210 it isdetermined if the temperature conditioning required flag has been setand if so the conditioning required pattern is lighted in block 212. Inother words, if any of the above-identified flags have been set, thenthe battery 22 displays the conditioning required pattern in a block212. The conditioning required display pattern, in one embodiment theinvention, alternates flashing the first and third LED's with the secondand forth LED's.

It should be noted that the flags checked in blocks 206, 208 and 210 arestored in the nonvolatile memory 142 of the battery 22 and the order inwhich they are checked is unimportant. If the smart battery 22 does notfind a critical error in a block 202 or a non-critical error in a blocks206, 208, or 210, then it displays in a block 214 the state of thecharge of the battery and then returns in a block 216 to the mainprocessing routine shown in FIG. 7A.

In one embodiment of the invention a relative state of charge thatincludes a “reserve factor” is displayed using the LED's 76 a-d. One LEDflashes if the relative state of charge is less than or equal to 0%; oneLED lights steadily if the relative state of charge is greater than 0%but less than or equal to 25%; two LED's light steadily if the relativestate of charge is greater than 25% but less than or equal to 50%; threeLED's light steadily if the relative state of charge is greater than 50%but less than or equal to 75%; and, four LED's light steadily if therelative state of charge is greater than 75%.

In computing the relative SOC for the display, a reserve factor, orerror margin, is used when computing the reserve capacity that the LED'swill indicate according to the equation:$\underset{\_}{{Equation}\quad 3\text{:}\quad {Display}\quad {SOC}\quad {equation}}$${{Display}{SOC}} = \frac{\left( {{SOC}_{1} - R} \right) \cdot 100}{100 - R}$

In this equation:

Display SOC is the value of SOC to display in percent. This value iscalculated.

SOC₁ is the present value of the calculated SOC in percent. This valueis calculated.

R is the value of the reserve capacity in percent. This value is aconstant and in one embodiment of the invention is 15 (representing15%).

As noted above, in addition to reporting the battery's condition to theuser through the lighted display 76, the smart battery 22 communicateswith other devices. The messages relating to the dynamic state of chargecalculations/adjustments are discussed above. External devices mayaccess the smart battery to retrieve information that it maintains aboutitself For instance, the smart battery 22 can report its state ofcharge, request maintenance, or indicate that it has reached the end ofits useful life and should be discarded.

The smart battery 22 reports its status through the communicationinterface 142 according to the routine shown in FIG. 11. In a decisionblock 222, the battery 22 checks whether the cycles conditioningrecommended flag 182 is set; in a decision block 224 the battery 22determines whether the cycles conditioning required flag 194 is set; ina decision block 226 the battery determines whether the timeconditioning recommended flag 190 is set; in a block 228 the batterydetermines whether the time conditioning required flag 194 is set; in ablock 230 the battery determines whether the temperature conditioningrequired flag 198 is set; and, in a block 232 the battery determineswhether the microprocessor reset flag has been set. If any of the flagschecked in a blocks 222, 224, 226, 228, 230, or 232 are set, aconditioning requested flag is set in a block 234.

The smart battery 22 then checks to see if any critical errors have beenlogged in the nonvolatile memory in a block 236. If a critical error hasbeen found, then a discard flag is set in a block 238. The flags set inblocks 234 and 238 are then communicated via the communication interface144 to the host devices in a block 240 in accordance with the SMBusstandard. It will be recognized by those of ordinary skill in the artthat the device receiving these flags will process them as necessary inorder to condition, charge or otherwise test the battery 22. Control isthen returned in a block 242 to the main processing routine of FIG. 7A.

In addition to sending information about its condition to externaldevices, the battery 22 can receive and process notifications from otherdevices via the communication interface pads 56 and communicationinterface 144. The notifications used in the SOC process are describedabove. Following conditioning, a battery maintenance and testing systemcan notify the smart battery 22 after the smart battery has beenconditioned. The routine implemented by the battery 22 when an End ofConditioning notification is received is illustrated in FIG. 12.Essentially, this routine resets all the non-critical error flags. In ablock 244, the cycles conditioning recommended flag 182 is cleared; in ablock 246 the cycles conditioning required flag 186 is cleared; in ablock 248 the time conditioning recommended flag 190 is cleared; in ablock 250 the time conditioning required flag 194 is cleared; and, in ablock 252 the temperature conditioning required flag 198 is cleared. Inaddition, the time since the last conditioning counter is cleared in ablock 256 and the cycle since last conditioning counter is set to thecurrent number of cycles the battery has been through in a block 258.Control is then returned in a block 260 to the main processing routineof FIG. 7A.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.Accordingly, it is not intended that the scope of the invention belimited by the actual embodiments describe above. Instead, the inventionshould be determined entirely by reference to the claims that follow.

What is claimed is:
 1. A method for self monitoring a rechargeablebattery's ability to reliably deliver charge to a host device, themethod comprising: dynamically calculating a state of charge (SOC) thatquantifies the ability of the rechargeable battery to deliver charge toa host device as charge is drawn from and supplied to the battery;charging the rechargeable battery until an end of charge message isreceived, the end of charge message indicating that the rechargeablebattery has stopped accepting charge; and adjusting the SOC to a fullcharge capacity value if the SOC exceeds the full charge capacity valuewhen the end of charge message is received by the rechargeable battery.2. The method of claim 1, further comprising: discharging therechargeable battery until an end of discharge message is received, theend of discharge message indicating that the rechargeable battery hasreached a nominal low battery threshold; adjusting the full chargecapacity by adding the SOC to the full charge capacity if the SOC isless than or equal to zero when the end of discharge message is receivedby the rechargeable battery; and resetting the SOC to a minimum chargevalue after dynamically adjusting the full charge capacity.
 3. Themethod of claim 2, further comprising not dynamically adjusting the fullcharge capacity by adding the SOC to the full charge capacity when theend of discharge message is received if any of the following conditionsis not met during a discharge cycle: (i) the rechargeable battery wasdischarged from a fully charged state; (ii) the rechargeable battery wasnot partially charged; (iii) an accumulated self-discharge value doesnot exceed a predefined percentage of an estimated initial full chargecapacity; and (iv) the rechargeable battery temperature did not exceed apredefined temperature limit.
 4. The method of claim 2, furthercomprising: setting a discard flag when the end of discharge message isreceived and the SOC is positive and exceeds a predefined error margin.5. The method of claim 4, further comprising adjusting the SOC with anefficiency coefficient.
 6. The method of claim 5, further comprisingadjusting the efficiency coefficient as the SOC changes.
 7. The methodof claim 6, further comprising adjusting the SOC with a self dischargerate.
 8. The method of claim 7, further comprising adjusting the selfdischarge rate to reflect for the time since the rechargeable batterywas last charged.
 9. The method of claim 1, wherein the SOC isdynamically calculated by a monitoring circuit using a discharging SOCequation.
 10. The method of claim 9, wherein the discharging SOCequation is:${SOC}_{1} = {{SOC}_{0} - \left\{ {K_{T} \cdot E_{D} \cdot \left( \frac{I_{D1} + I_{D0} + I_{B1} + I_{B0}}{2} \right) \cdot \left( \frac{t_{1} - t_{0}}{3600 \cdot C_{nom}} \right)} \right\}}$

the variable in the discharging SOC equation being defined as: SOC₁ is apresent value of the calculated SOC in percent; SOC₂ is a prior value ofthe calculated SOC in percent; K_(T) is a temperature coefficient ofdischarge current and has no units; I_(D1) is a present charge currentinto the rechargeable battery in amperes; I_(D0) is a prior chargecurrent into the rechargeable battery in amperes; I_(B1) is a presentbias current for the monitoring circuit in the rechargeable battery inamperes; I_(B0) is a prior bias current for the monitoring circuit inthe rechargeable battery in amperes; t₁ is a present time of themeasurements in seconds; t₀ is a prior time of the measurements inseconds; E_(D) is the efficiency of discharge in percent; 2 is anaveraging factor; 3600 is a constant conversion factor accounting fortime in seconds and capacity in amp hours; C_(nom) is a batterymanufacturer's capacity rating in AH; and SD_(T) is an amount ofcapacity lost due to self discharge in percent.
 11. The method of claim9, wherein the charging SOC equation is:${SOC}_{1} = {{SOC}_{0} + {\left\lbrack \frac{E_{C} \cdot \left( {I_{C1} + I_{C0} - I_{B1} - I_{B0}} \right) \cdot \left( {t_{1} - t_{0}} \right)}{7200 \cdot C_{nom}} \right\rbrack {}_{{SOC}_{0} < {FCC}}}}$

the variables in the discharging SOC equation being defined as: SOC₁ isa present value of the calculated SOC in percent; SOC₀ is a prior valueof the calculated SOC in percent; E_(C) is a efficiency of chargeacceptance in percent; I_(C1) is a present charge current into therechargeable battery in amperes; I_(C0) is a prior charge current intothe battery in amperes; I_(B1) is a present bias current for themonitoring circuit in the rechargeable battery in amperes; I_(B0) is aprior bias current for the monitoring circuit in the rechargeablebattery in amperes; t₁ is a present time of the measurements in seconds;t₀ is a prior time of the measurements in seconds; 7200 is a constantconversion factor accounting for averaging; C_(nom) is a batterymanufacturer s capacity rating in amp hours; and FCC is the full chargecapacity.
 12. The method of claim 1, further comprising maintaining alog of critical errors in the non-volatile memory, each critical errorindicating that the rechargeable battery may not be reliable and shouldbe discarded.
 13. The method of claim 12, wherein a critical error islogged if the number of cycles that the rechargeable battery has beenthrough exceeds a predefined maximum number of cycles.
 14. The method ofclaim 12, wherein a critical error is logged if an interval of the timethat the rechargeable battery has been in use exceeds a predefinedmaximum lifetime.
 15. The method of claim 12, wherein a critical erroris logged if the contents of a non-volatile memory of the rechargeablebattery have become corrupted.
 16. The method of claim 12, wherein acritical error is logged if the rechargeable battery receives anotification from another device that the rechargeable battery should bediscarded.
 17. The method of claim 12, wherein a critical error islogged if the full charge capacity is less than a predefined full chargecapacity minimum value.
 18. The method of claim 12, wherein anindication that the rechargeable battery may not be reliable and shouldbe discarded is displayed if a critical error has been recorded in thelog of critical errors.
 19. The method of claim 12, wherein a criticalerror is communicated by the rechargeable battery to a host device via acommunication interface.
 20. The method of claim 12, further comprisingdisplaying the ability of the rechargeable battery to reliably delivercharge to a host device by displaying an indication of the SOC of therechargeable battery.
 21. The method of claim 1, further comprisingmaintaining at least one non-critical critical error flag in anon-volatile memory of the rechargeable battery, each non-critical errorflag indicating that the rechargeable battery requires maintenance. 22.The method of claim 21, a cycles conditioning recommended flag is set ifa count of cycles experienced by the rechargeable battery exceeds acycles conditioning recommended interval.
 23. The method of claim 21, acycles conditioning required flag is set if a count of cyclesexperienced by the rechargeable battery exceeds a cycles conditioningrequired interval.
 24. The method of claim 21, a time conditioningrecommended flag is set if a time interval since the rechargeablebattery was last conditioned exceeds a cycles conditioning recommendedinterval.
 25. The method of claim 21, time conditioning required flag isset if a time interval since the rechargeable battery was lastconditioned exceeds a time conditioning required interval.
 26. Themethod of claim 21, an indication that the rechargeable battery requiresmaintenance is displayed if a non-critical error has occurred.
 27. Themethod of claim 26, wherein the indication that the rechargeable batteryrequires maintenance is only displayed when the non-critical error is ofa predefined type that indicates that maintenance is required.
 28. Themethod of claim 27, wherein the predefined type is a cycles conditioningrequired flag that is set if a count of cycles experienced by therechargeable battery exceeds a predefined cycles conditioning requiredinterval.
 29. The method of claim 27, wherein the predefined typeincludes a time conditioning required flag that is set if a timeinterval experienced by the rechargeable battery exceeds a predefinedtime conditioning required interval.
 30. The method of claim 27, whereinthe predefined type includes a temperature conditioning required flagthat is set if a cumulative time over temperature interval experiencedby the rechargeable battery exceeds a predefined temperatureconditioning required interval.
 31. The method of claim 26, wherein thenon-critical error is communicated to a host device via a communicationinterface as a request for maintenance.
 32. A smart battery apparatus,comprising: a smart battery housing; a user interface display areamounted upon the smart battery housing; a monitoring circuit mountedupon a circuit board for monitoring a state of charge (SOC) of the smartbattery and displaying the SOC on the user interface display area; and aplurality of electrically conductive rods coupled to the circuit boardin a manner that conducts an electrical signal through the electricallyconductive rods to the monitoring circuit.
 33. The apparatus of claim32, wherein the monitoring circuit has a central processing unit that isprogrammed to adjust the SOC to a full charge capacity (FCC) when a hostdevice communicates to the monitoring circuit that the host device hasdetected that the smart battery has stopped accepting charge.
 34. Theapparatus of claim 33, wherein the central processing unit is programmedto adjust the FCC if the SOC is less than or equal to zero when the hostdevice communicates to the monitoring circuit that the host device hasdetected that the smart battery has been fully discharged.
 35. Theapparatus of claim 32, wherein the monitoring circuit has a centralprocessing unit that monitors the smart battery's need for maintenance.36. The apparatus of claim 35, wherein the monitoring circuit is coupledto a non-volatile memory circuit and the central processing unitindicates that the battery requires maintenance by setting in thenon-volatile memory a cycles conditioning required flag in if a count ofcycles experienced by the rechargeable battery exceeds a predefinedcycles conditioning required interval.
 37. The apparatus of claim 35,wherein the monitoring circuit is coupled to a non-volatile memorycircuit and the central processing unit indicates that the batteryrequires maintenance by setting in the non-volatile memory a timeconditioning required flag that is set if a time interval experienced bythe rechargeable battery exceeds a predefined time conditioning requiredinterval.
 38. The apparatus of claim 35 wherein the monitoring circuitis coupled to a non-volatile memory circuit and the central processingunit indicates that the battery requires maintenance by setting in thenon-volatile memory a temperature conditioning required flag that is setif a cumulative time over temperature interval experienced by therechargeable battery exceeds a predefined temperature conditioningrequired interval.
 39. The apparatus of claim 35, wherein the centralprocessing unit communicates the need for maintenance to a host devicevia a communication interface that is coupled to the central processingunit.
 40. The apparatus of claim 35, wherein the central processing unitdetermines when the smart battery should be discarded by logging acritical error in a non-volatile memory that is coupled to the centralprocessing unit.
 41. The method of claim 40, wherein a critical error islogged by the central processing unit if a count maintained by thecentral processing unit of the number of cycles that the rechargeablebattery has been through exceeds a predefined maximum number of cycles.42. The method of claim 40, wherein a critical error is logged by thecentral processing unit if an interval maintained by the centralprocessing unit of the time that the rechargeable battery has been inuse exceeds a predefined maximum lifetime.
 43. The method of claim 40,wherein a critical error is logged by the central processing unit if aprogram content of the non-volatile memory has become corrupted.
 44. Themethod of claim 40, wherein a critical error is logged by the centralprocessing unit if the rechargeable battery receives a notification froma host device that the smart battery should be discarded.
 45. The methodof claim 40, wherein a critical error is logged by the centralprocessing unit if a full charge capacity is less than a predefined fullcharge capacity minimum value.
 46. The method of claim 40, wherein thecentral processing unit displays through the user interface and displayan indication of that the rechargeable battery may not be reliable andshould be discarded if the central processing unit has logged a criticalerror.
 47. The apparatus of claim 40, wherein a critical error iscommunicated by the smart battery to a host device via a communicationinterface.